Method for making a clad wire for an electric contact

Abstract

A clad wire for an electric contact is made by sofening a clad tape, which consists of at least a base metal and a surface layer of noble metal, by annealing, forming the softened clad tape into a cross sectional form of a circular arc, and cold-drawing the formed clad tape through a die having a desired cross sectional shape so as to provide a clad wire.

We claim: 
     
       1. A method for making a clad wire for an electric contact comprising the steps of softening a clad tape by annealing, said clad tape comprising a base metal and at least one surface layer of noble metal firmly bonded to said base metal, forming said softened clad tape into a cross sectional shape of a circular arc perpendicular to the longitudinal direction of said clad tape with said noble metal surface layer on the outside peripheral surface thereof, and normally cold-drawing said formed clad tape through a wire forming die having a standard section with the noble metal surface layer on the outer surface of the drawn clad tape, whereby there is provided a clad wire which is partially clad with said noble metal as a surface layer. 
     
     
       2. A method for making a clad wire for an electric contact as claimed in claim 1, wherein said clad tape has a ratio of thickness to width ranging from 1/3 to 1/5. 
     
     
       3. A method for making a clad wire for an electric contact as claimed in claim 1, wherein said clad tape is formed into said formed clad tape by being drawn through a forming die having the cross section of the circular arc. 
     
     
       4. A method for making a clad wire for an electric contact as claimed in claim 1, wherein said clad tape is formed into said formed clad tape by being rolled through a forming roll pair comprising a concave profile roller and a convex profile roller opposite to said concave profile roller. 
     
     
       5. A method for making a clad wire for an electric contact as claimed in claim 1, wherein said formed clad wire is drawn through a wire forming die having a cross section shape taken from the group of round, semiround, triangle, square and trapezoidal. 
     
     
       6. A method of making a clad wire for an electric contact as claimed in claim 1, wherein said noble metal surface layer of said clad wire is stretched around more than a half of the periphery of the cross section of said clad wire. 
     
     
       7. A method for making a clad wire for an electric contact as claimed in claim 1, wherein said clad wire is in two layers of a surface layer and a base metal layer, the material of said surface layer being selected from the group consisting of silver, silver alloys, gold, gold alloys, palladium alloys, platinum or platinum alloys, and the material of said base metal layer being selected from the group consisting of copper, copper alloys, nickel and nickel alloys. 
     
     
       8. A method for making a clad wire for an electric contact as claimed in claim 1, wherein said clad wire has two surface layers, a top surface layer and an intermediate surface layer, and a base metal layer, the material of said top surface layer being a metal selected from the group consisting of silver, silver alloys, gold, gold alloys, palladium, palladium alloys, platinum and platinum alloys, the material of said intermediate surface layer being a metal selected from the group consisting of silver, silver alloys, nickel and nickel alloys, and the material of said base metal layer being a metal selected from the group consisting of copper, copper alloys, nickel and nickel alloys.